1. Field of the Invention
The invention relates to a MIS (Metal Insulator Semiconductor) type field effect transistor configuring a semiconductor integrated circuit, and particularly to a MIS type field effect transistor, which is improved in source and drain.
2. Description of the Related Art
High performance of a field effect transistor has been achieved by microminiaturization on the basis of a scaling rule. However, in the field effect transistor whose gate length is not more than 15 nm, the source and drain whose thickness is as shallow as 10 nm and whose resistance is as low as 700 .OMEGA. are required. It is difficult to satisfy this requirement by an impurity diffused layer.
In recent years, a MOSFET wherein Schottky (metal to semiconductor) junction instead of a conventional PN junction is used for a source and a drain is proposed.
In the MOSFET of this Schottky source/drain structure, metal is used for the source and drain regions, so that an extremely shallow junction can be formed. Further, this Schottky structure has various advantages such as an extremely low parasitic resistance due to a low specific resistance, and is expected to fabricate a next generation field effect transistor.
However, in the MOSFET of this kind of Schottky source/drain structure, there is a problem that a large driving current is not provided due to a contact resistance caused by a Schottky barrier formed at an interface between a metal source/drain and a channel semiconductor. A Schottky source/drain structure that source and drain electrodes are offset with respect to a gate electrode is suggested (for example, Japanese Patent Laid-Open No. 2002-94058). There is a problem that a large driving current is not provided due to a contact resistance caused by a Schottky barrier in this device, too.
As discussed above, a field effect transistor having a Schottky source/drain structure is effective for realizing a shallow source/drain junction and decreasing a parasitic resistance. However, this kind of transistor has a problem that a large driving current is not provided due to an increase of a contact resistance caused by a Schottky barrier.